1. Field of the Invention
This invention relates to a lubricating oil for compressors of refrigerators using therein a hydrogen-containing halogenocarbon as a refrigerant (the oil being hereinafter referred to as "a refrigerator oil for use with a hydrogen-containing halogenocarbon refrigerant") and, more specifically, it relates to such a refrigerator oil which comprises a specific ester as a base oil and is superior in various properties.
2. Description of the Prior Art
Heretofore, as refrigerator oils, there have been usually used naphthenic mineral oils having a kinematic viscosity of from 10-200 cSt at 40.degree. C., paraffinic mineral oils, alkylbenzenes, polyglycol oils, mixtures thereof, and blends of these base oils and additives.
On the other hand, as halogeno carbon refrigerants used in refrigerators, there are utilized CFC-11, CFC-12, CFC-115, HCFC-22 and the like.
Of these halogeno carbon refrigerants, CFC-1, CFC-12, CFC-115 and the like in which all the hydrogen atoms of a hydrocarbon are replaced with halogen atoms such as chlorine atoms tend to break an ozone layer, and for this reason, the employment of these halogeno carbons is regulated under a law. Therefore, hydrogen-containing halogeno carbons, above all, hydrofluoro carbons such as HFC-134a and HFC-152a are increasingly employed in place of the CFC series. In particular, HFC-134a is similar in thermodynamic properties to CFC-12 which has been heretofore used in many refrigerators such as domestic refrigerators, air-conditioners and car air-conditioners, and thus HFC-134a is promising as the replaceable refrigerant.
The refrigerator oil must meet various requirements, and the compatibility of the oil with the refrigerant is extremely important from the viewpoints of the lubricating properties and the system efficiency of the refrigerator. However, the refrigerator oil comprising a base oil such as the naphthenic mineral oil, the paraffinic mineral oil or the alkylbenzene is scarcely compatible with a non-chlorine halogeno carbon such as HFC-134a. Therefore, if such a kind of refrigerator oil is used in combination with HFC-134a, a two-layer separation occurs at ordinary temperature, and oil return properties which are most important in the refrigerator system deteriorate. In consequence, refrigeration efficiency decreases or lubricating properties decline, with the result that a compressor tends to burn and other problems occur inconveniently. Hence, the employment of the above-mentioned oil in combination with HFC-134a is not practical.
In order to solve these problems, the present inventors have developed a polyglycol refrigerator oil which is much more excellent in the compatibility with HFC-134a as compared conventional known refrigerator oils, and have already submitted a patent application regarding this refrigerator oil (Japanese Patent Application Laid-open Nos. 1-256594, 1-274191 and the like). In addition, U.S. Pat. No. 4,755,316 discloses a polyglycol refrigerator oil which is compatible with HFC-134a.
On the other hand, the refrigeration lubricant which can be used in the compressor of the domestic refrigerator or the like is required to have high electrical insulating properties. Of the known refrigerator oils, alkylbenzenes and the mineral oils have the highest electrical insulating properties, but as described above, they are scarcely compatible with a hydrofluoro carbon such as HFC-134a. Furthermore, the polyglycol oil which is excellent in compatibility with HFC-134a is poor in electrical insulating properties inconveniently.
The present inventors have found that an ester having a specific structure is excellent in compatibility with a halogeno carbon such as HFC-134a and has high electrical insulating properties, and they have already filed a patent application regarding this ester (Japanese Patent Application No. 1-341245 and the like).
However, the above-mentioned ester is excellent in various characteristics but brings about hydrolysis, and for this reason, it is not always suitable for devices such as a refrigerator and a car air-conditioner which are required to be driven keeping up a high reliability for a long period of time. Therefore, it is strongly desired to develop a refrigeration lubricant having high compatibility with a hydrogen-containing halogeno carbon such as HFC-134a, satisfactory electrical insulating properties, and stability to hydrolysis.
Heretofore, an ester synthetic oil is known as a synthetic oil having excellent heat resistance and used as a usual industrial lubricating oil or the like. However, this kind of oil involves the above-mentioned problem of the hydrolysis, and in consequence, the development of an ester synthetic oil having the excellent stability to the hydrolysis is largely expected.
An object of the present invention is to provide a refrigerator oil mainly comprising a specific ester and having high compatibility with a hydrogen-containing halogeno carbon such as HFC-134a, high electrical insulating properties, and the stability to hydrolysis.